Similarities and differences in the ordering at short and long ranges in a NaNbO₃ based Pb-free smart system: a key to functional properties

In this study, we have investigated the crystal structure of the solid solution of antiferroelectric NaNbO 3 (NN) with ferroelectric Ba 0.9 Ca 0.1 TiO 3 (BCT), i.e. (1− x )NN- x BCT for 0 ⩽ x ⩽ 1.0 using High-resolution powder x-ray diffraction (HR-XRD) data, dielectric measurements in conjunction with Raman spectroscopic studies. The investigation of long-range structural phase transitions as a function of composition( x ) using x-ray diffraction is complemented by short-range structural insights from Raman spectroscopy. The incorporation of BCT disrupts the delicate antiferroelectric ordering of NN and stabilizes various ferroelectric phases with increasing BCT content( x ). At x = 0.10, the simultaneous presence of two ferroelectric phases viz., Pmc2 1 and Amm2, results in a threefold rise in remanent polarization compared to off-boundary compositions. The composition with higher BCT content (i.e. x ⩾ 0.50 ) has shown the anomalous existence of two long-range cubic structures, both of which are characterized by Pm 3 ¯ m space group. In spite of having a two-phase long-range centrosymmetric structure, we have observed a slim Polarization vs. Electric field(P-E) hysteresis loop for 0.50 ⩽ x ⩽ 0.80 . This contrapositive behavior (i.e. hysteresis loop in a centrosymmetric structure) has been attributed to the correlations among local static polar distortions of rhombohedral type ascertained using Raman spectroscopy. The coexistence of two ferroelectric phases at room temperature(for x = 0.10) and a slim hysteresis loop (for 0.50 ⩽ x ⩽ 0.80 ) make these compositions potential ingredients for applications in ferroelectric memory and energy storage devices.